A few months ago, we upgraded our Netgear router's firmware. Immediately, we started having trouble connecting to the internet. Each time this problem would happen, every device in the house would stop being able to make new connections to the internet. For example, you couldn't open new pages in the browser, but if Skype was running when the problem happened, you could keep talking to people. The only solution to this problem seemed to be resetting the router to factory defaults.
Eventually, we solved this problem by just downgrading the router firmware. A while later, we got a new Netgear router. Almost right away, the new router started having exactly the same problems as the old one did on current firmware. The network connection would stay active and the computer would say it had an internet connection, but you couldn't do anything online except for using Skype.
We eventually figured out that this happens every time our HP printer gets onto the network. Any time the printer gets onto the wireless network, the whole network stops connecting to the internet almost completely. The only thing that will fix it at that point is to reset the router to factory specs, and unplug the printer so it can't get back onto the network.
The Netgear router has the latest version of the firmware, but the printer/scanner is very old. It looks to me like this problem is probably a result of a firmware conflict between the printer and the router, but I'm not sure how to fix that problem.
Here's some additional information:
Printer: HP Photosmart C4780
Router firmware: V220.127.116.11_1.0.17 (Stock, up to date firmware)
Why would the printer getting on the network cause the router to not be able to access the internet correctly until it was reset? What can be done to allow the printer to be on the network without breaking the network for all other devices?
Edit: One other thing that happens during this internet problem is that multiple computers in the house display an "IP conflict" message repeatedly, and extremely frequently (as often as every five to ten minutes, and every time a connection to the wireless is made).